The present invention relates to electrode-carrying catheters, and more particularly to an inexpensive and reliable electrode-carrying catheter and a method of making the same.
Electrode-carrying catheters as well know in the medical art and find diagnostic and therapeutic utility in a wide variety of different applications. For example, mapping catheters are used diagnostically to produce a wave function of the heart's electrical impulses so that a doctor can determine proper functioning or fault, and location of the fault, in the heart. Ablative catheters are used therapeutically to destroy tissue in the heart causing tachycardia, utilizing radio frequency current catheter ablation. Such catheters are also used for heart pacing purposes and for analgesia in various parts of the body. Depending upon the particular application for which the catheter is used, it may be desirable for the catheter to carry one or more side electrodes, one or more end electrodes, or a combination thereof. The use of a plurality of smaller electrodes rather than a single large electrode enables higher current densities to be obtained and frequently enables superior electrical contact with the tissue, both of these being highly desirable factors in connection with ablative catheters in particular, where larger areas of radio frequency ablation in the tissue are desirable.
Electrically conductive wires have never proven to be entirely satisfactory as the electrodes since a functional electrode requires a much larger surface area than can be provided by a flexible wire. Further, unless provisions are made to fix the wire relative to the catheter tubing, it is extremely difficult to ensure that the wire is held in place so as to assure a reliable electrical contact. While a wire could be held in place by use of an electrically conductive adhesive securing the wire to the tubing, it would be extremely difficult to create an electrode by applying an adhesive in a thin layer over a large surface area, as would be necessary to ensure that the electrode layer is flexible.
While a biocompatible conductive paint as an electrode has the advantage of being easily applied in an extremely thin layer to the tubing outer surface by printing techniques, so as to ensure flexibility thereof and cover the wire, there are other problems associated with such conductive paint. While the flexible, thin layer of conductive ink painted on the tubing outer surface forms a good electrical connection with the wire, the conductive paint does not form a reliable physical connection with the typical wire, as necessary to ensure that the passage of the catheter through the human body along the guidewire to the proposed working site does not to some degree remove, separate or abrade away the thin layer of conductive paint.
Typically electrode-carrying catheters are made by applying metal strips on the outer side and/or distal (front) surfaces of a flexible tubing of non-conductive plastic, each side strip acting as a side or ring electrode and each distal strip acting as an end electrode. The presence of the metal strips limits the natural flexibility of the tubing so that the catheter is not of high flexibility throughout its entire length, and this presents problems in threading the catheter into the human body over a guidewire since the diminished flexibility may limit the ability of the catheter to conform to the travel path defined by the guidewire, leading to blood vessel trauma. Nonetheless, such catheters carrying ring electrodes are in favor because of the high level of reliability of the electrical connections therein.
The conventional processes for forming ring or metal band electrodes flush with the outer surface of a catheter are arduous, time-consuming and/or require further processing. For example, in one process, metal bands and sleeves therebetween are slipped over the tubing outer surface with the sleeves maintaining the appropriate spacing between adjacent electrodes; this requires the use of additional pieces (namely, the sleeves) and an arduous assembly process. Another process requires the tubing to be stretched to lower the outer diameter thereof, metal bands placed over the stretched tubing and disposed in appropriate spatial relationship, and the tubing then heated and released. The metal bands sink into the heat-softened tubing outer surface as the tubing resumes its original configuration (except where the metal bands are embedded therein). This technique requires additional stretching, heating and cooling steps.
Accordingly, it is an object of the present invention to provide in one embodiment an electrode-carrying catheter having a ring or metal band electrode thereon flush with the catheter outer surface.
Another object is to provide such a catheter which can mount a large number of electrodes.
A further object is to provide such a catheter wherein there is a reliable adhesive-free electrical contact between an electrode and any conductive wire extending from the proximal end to the electrode, the electrode has a sufficiently large surface area for electrode functioning, and all exposed surfaces are biocompatible.
It is also an object of the present invention to provide such a catheter which is easily and inexpensively manufactured.
It is another object to provide processes for the manufacture of such catheters.